Kotlin DSL

request.kt

data class Request(
    val method: String,
    val path: String,
    val headers: Map<String, String>
)

class RequestBuilder {
    private lateinit var method: String
    private lateinit var path: String
    private var headers = mutableMapOf<String, String>()

    fun method(get: () -> String) = apply {
        method = get()
    }

    fun path(get: () -> String) = apply {
        path = get()
    }

    fun header(get: () -> Pair<String, String>) = get()
        .also { (key, value) ->
            headers[key] = value
        }

    fun build(): Request = Request(method, path, headers)
}

fun request(builder: RequestBuilder.() -> Unit) = RequestBuilder().apply(builder).build()

val request = request {
    method { "GET" }
    path { "/path" }
    header { "name" to "value" }
}

println(request) // Request(method=GET, path=/path, headers={name=value})